1. Technical Field
The present invention relates to a glass antenna provided on a glass in an opening in a vehicle body.
2. Background Art
Glass antennas are widely used because the antennas have superior designs, reduced damage concerns, less wind noise, and other reasons unlike conventional rod antennas. A glass antenna used on a window glass is well-known, as disclosed in Patent Literature 1 below. FIG. 11 shows the glass antenna disclosed in Patent Literature 1.
FIG. 11 hereof shows a space-saving monopole glass antenna 110 having an increased reception gain across a wide range from FM radio broadcast waves to TV broadcast waves and UHF broadcast waves. The antenna 110 includes a horizontal strip 111, a horizontal strip 112 and a fold 113 interconnecting the strips 111, 112. The horizontal strip 111 extends substantially horizontally from a feed point 114. The horizontal strip 112 is substantially parallel to the horizontal strip 111.
Among known glass antennas is a grounded glass antenna as disclosed in Patent Literature 2 below. The grounded glass antenna disclosed in Patent Literature 2 has an impedance designed to approximate to a characteristic impedance of a feeder line of the antenna without use of an impedance matching circuit. FIG. 12 hereof shows the glass antenna disclosed in Patent Literature 2.
In FIG. 12, the glass antenna 120 includes an antenna pattern including a substantially linearly extending first element 121 and a second element 123 extending in substantially parallel to the first element 121. The antenna pattern also includes a folded portion 122 interconnecting the first element 121 and the second element 122. The glass antenna 120 further includes a feed point 124 connected to a distal end of the first element 121, a ground point 125 connected to a distal end of the second element 123, and a connecting wire 126 for grounding the ground point 125 to a vehicle body.
However, it is difficult to design the glass antennas disclosed in Patent Literatures 1 and 2 to provide a desired resonance frequency for improving reception capability when the glass antennas are mounted on glasses in vehicle windows having small opening areas of, for example, less than 0.15 m2. This is because the opening areas of the vehicle windows are so small that the antenna element cannot be long enough to allow addition of a bypass pattern. Recently, a vehicle quarter window to which is attached an antenna has been required to have a reduced surface area if the quarter window is used in, particularly, so-called mini-vans, sport utility vehicles (SUVs), and the like.
A glass antenna designed to be mounted on a glass having a small surface area is known as disclosed in, for example, Patent Literature 3 below. FIG. 13 hereof shows the glass antenna disclosed in Patent Literature 3.
In FIG. 13, the glass antenna 130 disclosed in Patent Literature 3 includes a single feeder terminal 131 connected to a receiver, first and second ground terminals 132, 133 connected to electrical conductors 140 in an opening in a glass window of a vehicle, and a single antenna element including conductive elements 134, 135, 136 connected to the feeder terminal 131 and the first and second ground terminals 132, 133.
In the antenna disclosed in Patent Literature 3, the addition of the ground terminals minimizes decrease in antenna impedance, and thus the glass antenna can provide adequate reception capability even when attached to a small glass window.
However, the antenna disclosed in Patent Literature 3 has a large number of terminals, the feeder terminal 131 and ground terminals 132, 133, etc. attached to the glass surface, as well as a large number of feeder lines. Material cost and assembly work are therefore created, resulting in a cost increase.
There has been a demand for a glass antenna providing improved reception capability without requiring an increased cost even when the glass antenna is installed in a small opening of a glass window.